Car and truck navigation systems based on global positioning system (GPS) receivers have become indispensable aids for both business and pleasure driving. Such systems do not work well, however, when signals from GPS satellites are obscured or unavailable as may happen when driving in a tunnel or urban canyon environment. To combat problems from GPS signal loss, inertial measurement units (IMU) are combined with GPS receivers to provide dead reckoning as a supplement to satellite navigation.
In typical GPS+IMU systems a yaw gyro estimates rate of change of heading while a tachometer counts revolutions of a transmission shaft to estimate speed. The need for a mechanical tachometer is often inconvenient, however. What is needed is a cordless GPS+IMU system in a box that does not require external wired sensors.